The Yeast Genetic Stock Center (YGSC), located in the Department of Molecular and Cell Biology of the University of California at Berkeley, serves as a depository and source of singly or multiply-marked genetically-characterized strains of the yeast Saccharomyces cerevisiae. The strains in the collection (more than 1,000) bear one to several mutant loci encompassing a wide range of functions and requirements of this eukaryotic organism. The strains are available to the scientific community both here and abroad, and are widely used for basic and applied research by teaching and research institutions and by industry. Strains are stored as dry milk paper replicas at 4 degrees C for easy low-cost dissemination; as a back-up supply they are stored in 20% glycerol at -75 degrees C. Strains are checked periodically for correct genotype and for ploidy and returned to storage. Every effort is made to preserve as much as possible the authenticity of the strains, thus assuring a reliable source of genetic markers and backgrounds. New strains bearing markers that are well characterized and of general interest are solicited from scientists; new strains are also constructed at the YGSC to facilitate the use of the collection or to be used in implementing new methodologies. A catalogue of strains and pertinent information is published every 3 to 4 years. For the past few years the Yeast Genetic Stock Center has participated in the collation and publication of the Genetic and Physical Maps of the Yeast Saccharomyces cerevisiae, and this activity will continue in the future. The Yeast Genetic Stock Center has been unofficially in operation since the early 1960's; it was funded by the National Science Foundation from 1972 until September of 1987, when funding was undertaken by the National Institutes of Health. A fee that is charged for the strains provides additional funds necessary for the operation of the Stock Center. One of the major additional goals of the YGSC is to create a database of the Stock Center and to make it available on-line to the scientific community. A major portion of the information on the Stock Center has already been added to this database. Mapping information accumulated for the publication of the genetic and physical maps of the yeast Saccharomyces cerevisiae has also been entered into this database and programs have been developed to correlate these two pools of information; when these become available to the general yeast genetic community, it should improve the utility and ease of use of the YGSC.